Cracking occurs in the first step of gaseous reduction of hematite iron ore, to magnetite, and can lead to the formation of fine material, with deleterious effects on operation of shaft furnaces. To study this, samples of three ore types from the Northern Cape iron ore field in South Africa, and one blended ore from this region, were studied. The methods were high temperature microscopy (during reduction) and quantification of fines formation following reduction disintegration tests. The ore types do differ significantly with regards to their propensity to form fines. Although disintegration is clearly triggered by reduction, no direct correlation could be established between the degree of reduction and the amount of fines generated. Reduction disintegration increased with higher hydrogen percentages (.5%) in the reduction gas, and at higher temperatures (in the 500-700uC range). Disintegration of the samples decreased at temperatures .750uC. There was no correlation between the presence of gangue minerals and fines formation.
An analytical method based on high resolution mass spectrometry coupled with liquid chromatography (LC-HRMS) for 25 quaternary phosphonium compounds (QPCs) and derived phosphine oxides (POs) was developed and validated. To investigate the occurrence and fate of QPCs in the aquatic environment, water, suspended solids and sediments from the rivers Rhine and Elbe (upper and middle Elbe as well as tidal Elbe) were analyzed, as well as samples from tributaries bearing significant loads of QPCs. For the first time, the quaternary phosphonium compound tetrabutylphosphonium (BuP) was detected. In the river Elbe concentrations were determined of up to 4700 ng/L (surface water) and 1000 μg/kg (sediment), respectively. Analysis of a time series of suspended solids (2005-2015) showed that QPCs have been present in the Elbe and Rhine catchment for at least one decade, with partly rising tendency. A degradation experiment with Rhine sediment revealed that triphenylphosphonium compounds (R-PhP) and BuP are persistent in contact with sediment and suspended solids and tend to sorb onto sediment particles. Toxicological studies (reactive oxygen species (ROS) after substance exposure, Ames test, Micronucleus test, determination of cytotoxicity) with selected QPCs confirmed that all of them exhibit cytotoxicity and some even genotoxic potential at elevated concentrations, which emphasizes the need for an emission regulation of these compounds.
View related articles View Crossmark dataConclusions: These results suggest that QDs can induce moderate or low oxidative stress. The higher results observed in fish exposed to 10 ppb and 100 ppb of QDs can be due to QDs aggregation occurring at higher QDs concentrations, which can also affect the bioavailability of toxic ions released. Therefore, in this preliminary study, the lower concentrations of QDs seem to be more hazardous to Zebrafish.
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